The Clinical Core will provide a common mechanism through which study subjects are characterized, and subject and family information (including biologic samples) is collected. Centralizing and coordinating these activities in the Clinical Core will create efficiencies for the planned projects and should stimulate additional collaborations between STAART autism researchers as well as, to a limited degree, researchers not funded by STAART. A shared core dataset including basic descriptive information on all potential participants in the STAART studies will be generated. In addition, the core will assist in project-specific data management and statistical analyses. Although there will be two sites for the clinical core (Kennedy Krieger Institute and Children's National Medical Center), the operations of the clinical activities complement each other and are conceptually similar. Specific objectives of this core include: 1. identifying and recruiting STAART research participants; 2. determining eligibility of participants; 3. conducting diagnostic assessments of subjects; 4. conducting inter-rater reliability trials for autism diagnostic assessments; 5. monitoring the fidelity of test administration; 6. conducting outcome data collection; 7. facilitating the collection and distribution of biological samples; 8. providing data storage and data management support.